The present invention relates to an axial flow fan with a strengthened coupling between the impeller blades and boss.
In the axial flow fan, the entire fan motor is flat in shape in order to mount the motor structure in the center of the fan. Because of this, the volume required for installation is small and the fan can be mounted simply on the side wall of an equipment, and so fans of this type are widely used for cooling in office automation equipment.
In normal axial flow fans, the stator of the motor passes through and is held in place by supporting arms in the center of a shallow round or square shaped cylindrical frame. The rotor rotates freely around the outside of this stator, and the impeller blades extend from this rotor in the direction of emission. The rotor causes the blades to revolve and causes air to flow in the axial direction of the frame. Normally, when the impeller blades are made from plastic resin, the shaft in the center of the stator is coupled to the boss in the center of the impeller shaft section by molding.
Conventionally, it has been usual to apply knurling to the molded resin shaft with the aim of reducing vibration during rotation, firmly fixing the shaft and increasing the strength of the bond between blade section boss and shaft. However, in cases where the ambient temperature is high and operation is carried out for a long time, heat generated by the rotor and stator causes the shaft to grow hot and expand by a very small amount. After operation is stopped, the shaft cools and shrinks back to its original size. When this process is repeated, the heat of the shaft during rotation cause the resin to soften and worsens the perpendicularity of the shaft in relation to the blades. The socalled shaft inclination and the rotational balance of the blades deteriorates, causing vibration during rotation.
The present invention is directed to overcoming the above disadvantages. This objective is accomplished by providing an axial flow fan consisting of impeller blades mounted in a rotor of the motor, by which the shaft supporting the rotor and the boss holding the blades are more firmly coupled, thus ensuring a longer service life for this coupling.